Multichannel pulse communication system



0d# 28, 1947- P. K. CHATTERJEA ET AL 2,429,608

I MULTICHANNEL PULSE COMMUNICATION SYSTEM Filed Feb. 16. 194s `WGA/IM .SOURCES Z i Harney Patented Oct. 28, 1947 MU LTICI-IAN N EL PULSE COMMUNICATION SYSTEM Prafulla Kumar Chatterjea and Leslie Wilfred Houghton, London, England, assignors, by mesne-assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application February 16, 1943, Serial No. 476,070

In Great Britain March 12, 1942 2 Claims. (Cl. 179-15) be selected at the receivingV end: so permitting the system to be very flexible as regards choice of channel. In the case of a radio link, it is usual to employ one carrier frequency and then to divide the permissible modulation frequency band into sub-bands, each sub-band corresponding to a separate'channel. Formaximum flexibility it is essential that the receiving end of such a radio link be capable of selecting any desired channel to do which a complete set of separating units i. e. filters or like units are required, eachy adjusted to its appropriate channel.

The present invention provides a Vcommunication system in which a single carrier frequency is employed, and a multiplicity 0f signals are contained in the signal used for amplitude modulating this frequency and, at the receiving end of such a communication system any channel may be selected at will, Without the duplication of terminal equipment, or with a minimum of additional equipment for contemporaneous reception of individual channels.

Accordingly the invention provides a multichannel communication system of the kind in which a complex Wave-form consisting of all the signal waves of the various channels modulates a carrier wave characterised in thisthat each of said channels comprises a pulse train of the same pulse repetition frequency and whose phases or moments of occurrence are displaced relatively to each other, andthe pulse train of each channel is modulated in amplitude bythe signal wave allotted to that channel.

The invention also comprises a multi-channel communication system of the kind referred to in the preceding paragraph in which the pulses of a pulse train of a channel are generated at the instant of maximum amplitude of a repetitive wave-form, the waves controlling the pulses of the different channels being displaced in phase relatively to each other.

The invention further comprises a receiver for the waves transmitted in a communication sys- Atem referred to in either of the tWo preceding paragraphs,and comprises means for obtaining from the received wave, a controlling wave of frequency equal to the pulse repetition frequency of a channel, and for applying said controlling wave to a receiver for the complex signal wave modulated carrier wave and which is normally inoperative, to render said receiver operative at moments corresponding to the maximum amplitude of said controlling wave as to render said receiver operative at moments corresponding to a particular channel. Where only one receiver is provided for all the channels, an adjustable phase shifting device is provided to adjust the phase of said controlling wave so as to render the v receiver selectively operative for any one channel.

' ceiver for use in conjunction with the transmitter 'cept insofar as it affects thev total power of the Where a receiver is provided for each channel, means are provided for adjusting the phase of the controlling wave applied to each receiver so that each receiver receives an allotted channel. Each receiver may have its own separate phase adjusting device.

'I'he y'invention will be explained in more detail in the following description of one embodiment thereof, taken in conjunction with the accompanying drawings.

In the said drawings:

Figs. 1, 2 and 3 are explanatory diagrams;

Fig. 4 shows diagrammatically an arrangement for generating a multiplex signal according to the invention;

Fig. 5 shows diagrammatically a suitable receiver for use in conjunction with the transmitter Vshown in Fig. 4 and Where only one receiver is provided and only one channel is selected at any one time;

Fig. 6 shows diagrammatically a suitable reshown in Fig. 4 and where any of the channels maybe received contemporaneously.

According to knownr technique, it is possible to transmit a given signal in the form of a series of short duration pulses by means of open wire or concentric transmission lines, wave guides or radiation, this said series or train of pulses being appropriately modilied by the signal. Fig. 1 of the drawings shows such a train, in which the signal is caused to modify, or modulate the pulse amplitude. The repetition frequency of the pulse train is determined by the maximum frequency contained in the signal to be transmitted, and the duration of each pulse is unimportant eX- transmitted signal, apart from its relationship to the inherent signal-noise ratio improvementobtainable in all vpulse systems.

One known method of generating a train of pulses is `to cause one pulse to be formed per cycle of a repetitive wave-form, such as a sinusoidal, or a sawtooth wave-form. For convenience, reference will here be made to a sinusoidal waveform as shown in (a) Fig. 2 of the drawings where a pulse is shown to be generated at each positive maxima as at (b) Fig. 2. Let the pulse repeti-f tion frequency, governed by the highest frequency component of the signal to be transmitted, be fp, then, referring to Fig. 2, it will be seen that one pulse is generated per cycle of fp. This pulse train can be made to contain one signal, by causing the amplitudes of the pulses to be modulated by that signal. If now another pulse train is generated, consisting of pulses having a repetition frequency of fp, but with pulses which occur at a diiferent instant to that shown in Fig, 2, then it will be possible to modulate this second train with a different signal. This process may obviously be repeated until the whole time interval of one cycle of frequency fp is occupied by pulses, as shown in Fig. 3 of the drawings, each of which can be made to contain an individual signal. (b) Fig. 3 shows the maximum number of pulses obtainable for a given time duration per pulse relative to fp at (a) Fig. 3 while (c) Fig. 3 shows the same pulses as they might appear when modulated, one signal being contained in pulses A, A', etc. or B, B', etc. The resulting wave shape shown in (c) Fig. 3 then constitutes the final multiplex signal wave used for` modulating a high frequency carrier, in the known manner, Whilst positive pulses only have been mentioned,

it will be understood that positive and negativeY pulses may be used, for example as in the case in which pulses are derived at the maximum negative and positive amplitudes of the sinusoidal wave shown at a, in Fig.r2. The pulse repetition period would then of course be 2fp and the pulses A, B, C and A', B', C' Fig. 3 would be alternatively positive and negative. In the following description however, it will be assumed that a pulse is produced only at the maximum positive amplitude of the controlling pulse generating wave (a Fig. 2)

An arrangement for generating such a multiplex signal as hereinbefore described is illustrated diagrammatically in Fig. 4 of the drawings, in which l represents an oscillator generating a suitable fundamental frequency.

The output from I is fed to harmonic generator 2 where the required harmonic is extracted for providing a sinusoidal output of frequency fp which is then fed to units 3, 4, 5, B and 1 each of which is a circuit for giving a different phasing to fp such that, starting from 3, the positive half cycles of each output is caused to occur at successive equal intervals of time throughout one cycle of fp. Each of these outputs, is then used for generating a pulse, the duration of which is, in this case, a fifth of the duration of one cycle of fp, each pulse occurring at the positive (or negative) peak of a cycle as shown in Fig. 2. The circuits for performing this, operation are for 3, unit 3, for 4 unit 9, etc. as shown in Fig. 4. Units 8, 9, I, II and l2 also provide meansv for modulating the generated pulses by the appropriate signal fed into each circuit from the corresponding terminals 8a, 9a, IIJa, IIa and I2a. The outputs of 8, 9, Ill, II and I2 are then fed in sequence to unit I3 giving a waveform similar to that shown at c in Fig. 3. At the same time,` however, a part of the output, from I. is also fed to I3 continuously giving a final lsignal which is then used to modulate a carrier transmitter according va transmission is shown schematically in Fig. 5

of the drawings where I4 represents a receiver of known type according to the transmission medium and which will give the waveform produced by unit I3 Fig. 4 as its rectified output. From this signal, is then extracted the single frequency initially generated by unit I Fig. 4 by means of a low pass lter I5, then unit I6, which is similar to unit 2 Fig. 4 generates the required harmonic to produce a controlling wave of frequency fp, which is then phased to the required degree by II depending on the individual signal channel required and from this output unit I8 generates a pulse of the same duration and relative phasing as that of the corresponding channel to the transmitter. Unit I9 is a special amplifier insofar that it is normally overbiassed so as to pass no signal except when a positive pulse from I8 is applied to it. To this amplifier is fed the output from I4 from which will therefore be selected only those amplitude changes appertaining to the channel represented by the pulse output from I8. The resultant output is therefore a train of amplitude modulated pulses similar to those generated at the transmitter for this particular channel, and thesignal contained in them can then be extracted by known pulse demodulation means or any low pass filter. Unit I1 can be made to correct for any time delay introduced by circuits I5, I6 and I8 and by simple pre-set circuits and switching it is readily possible to select any required signal channel.

In the case where contemporaneous reception of all the individual channels is required, an arrangement as shown in Fig. 6 of the drawings may be employed. In this figure, 20 represents the known type of receiver. As explained in connection with I5, I6 Fig. 5, low pass filter 2| and harmonic generator 22 produce the required control voltage of frequency .fp which asy at the transmitter is then fed into the phasing circuits 23, 24 2'I, and thence to the corresponding pulse generators 28, 29 32. These pulses are then fed to their respective amplifiers 33, 34 31 to each of which is also fed the output from receiver 20, so that each pulse selects its appropriate portion of the transmitted complex signal which is obtained at terminals 33a' 34a 31a. A point to note here is that units 28-32 are identical as are also units 33-31.

Limitation of the frequency spectrum occupied by such a transmission as herein described can cycles per sec, This, example brings. out one advantage of this system as compared to that of maximum frequency range required by such a system is double that of the system according to the present invention.

Apparatus and circuit arrangements for carrying out the functions of the units represented by rectangles in the drawings are numerous and well known to those versed in the art and specic details are not considered necessary for the understanding of the present invention. The harmonic generators 2, I6 and 22 may, for eX- ample, be of the type described in U. S. patent to Kendall 1,446,752, issued February 27, 1923. The low-pass filters l5 and 2| may be of the type described in U. S. patent to Campbell 1,227,113 issued May 22, 1917. The normally blocked ampliiiers I9 and 33 to 37 may, for example, be of the kind shown in Fig. 1 of U. S. patent to Deloraine and Reeves 2,262,838, issued November 18, 1941. The phase changing devices 3 to '1, I 6 and 23 to 21 may, for example, be of the kind described in U. S. patent 2,147,728 to Wintringham issued February 21, 1939, and the pulse generators such as I8, 218 to 32 may be similar to like components disclosed in U. S. patent 2,266,401 to Reeves, issued December 16, 1941.

Whilst specific embodiments of the invention have been described, others falling Within the scope of the appended claims Will occur to those skilled in the art. For example, in the arrangement shown in Fig. 6 any one of the series of units 23, 28-33, etc., may be arranged to receive any of the channels by appropriately adjusting the phase adjuster 23, etc. Furthermore one of the channels may be used as a pilot channel for a call signal, and-if a telephone termination is used, the pilot channel may be arranged to be brought into use when the receiver is removed from its support or hook.

What is claimed is: 1. In a multi-channel communication system comprising individual channels transmitting cyclically and successively for a fraction of the cycle period, means for producing the frequency of said cycle period, a plurality of phasing devices, said frequency being applied to said phasing devices, said phasing devices being so adjusted that the positive alternations in the outputs of said devices occur at successive equal intervals of time throughout one cycle of said frequency, a plurality of pulse generating means controlled by said phasing devices so as to produce trains of pulses occurring at the positive or negative peaks of the outputs of said phasing devices, means for amplitude modulation of each pulse train with its respective signal wave, a receiving station comprising a detector, a plurality of phase changing devices, means for applying the received signal to said phase changing devices, a plurality of pulse generators, means for applying said received signal through said phase changing device to a corresponding pulse generator, a plurality of normally blocked ampliers, means for applying the detector output to all of said ampliers, and means to unblock each amplier to the pulse received in its predetermined channel.

2. In a multi-channel communication system comprising a plurality of transmitting channels at the transmitting station, means for generating pulse trains relatively displaced in time and of the same pulse repetition frequency, a source of signals for each channel, an amplitude modulator for each channel, means for impressing on said amplitude modulator of each channel one of said pulse trains, a transducer having input and output circuits, means for modulating said transducer with the complex waves from said amplitude modulator, said transducer being adapted to impress its output upon a transmission medium, and comprising at the receiving station, means for receiving said complex Waves, means for deriving from the received waves a train of variable amplitude pulses of the same repetition frequency, said pulses being staggered with respect to time as the amplitude modulated signal pulses of a predetermined channel, a normally blocked receiver, means for impressing received waves therein and means to unblock said receiver with said received waves in accordance with the corresponding channel arrangement of the transmitter and receiver.

PRAFULLA KUMAR CHATTERJEA. LESLIE WILFRED I-IOUGHTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,395,467 Deloraine Feb. 26, 1946 913.363 Crehore Feb. 23, 1909 1,512,361 Peterson Oct. 21, 1924 2,007,809 Nicholson July 9, 1935 2,172,354 Blumlein Sept. 12, 1939 2,055,309 Ramsey Sept. 22, 1936 2,113,214 Luck Apr. 5, 1938 2,272,070 Reeves Feb. 3, 1942 2,352,634 Hull July 4, 1944 1,928,093 Coyle Sept. 26, 1933 2,048,081' Riggs rJuly 21, 1936 2,213,941 Peterson Sept. 3, 1940 2,282,046 Goldsmith May 5, 1942 2,227,108 Roosenstein Dec, 31, 1940 1,530,666 Hammond, Jr Mar. 24, 1925 1,979,463 Goshaw Nov. 6, 1934 2,082,877 Durand June 8, 1937 2,268,081 Felgel-Farnholz Dec. 30, 1941 2,057,773 Finch Oct. 20, 1936 2,146,876 Zworykin Feb. 14, 1939 2,204,375 Morrison June 11, 1940 2,257,562 Branson Sept. 30, 1941 1,742,902 Deloraine et al. Jan. 7, 1930 FOREIGN PATENTS Number Country Date 555.993 Great Britain Sept. 15, 1943 

